In 1771, Joseph Priestley conducted an experiment that demonstrated the symbiotic relationship between plants and animals. When he placed either a mouse or a plant alone in a sealed glass container, it soon died. But when he placed the mouse and plant together in the container, they survived. He noted that each somehow made the air breathable for the other. In September 2011, Iain Stewart, professor of geoscience at Plymouth University, conducted a scaled-up version of this famous experiment. Instead of a single plant he used 150 plants, and instead of a mouse he used a person — himself.

Stewart conducted his experiment at the Eden Project, a large, botanical-themed visitor attraction in St. Austell, Cornwall. His container was an airtight Perspex tank, 8 meters long, 2 meters wide, and 2½ meters high. The plants inside it included miscanthus, banana plants, maize, and a variety of tropical herbs. He hoped to find out if he could survive for 48 hours sealed in the tank with the plants. The event was filmed by the BBC as part of a documentary, How Plants Made the World. Eden Project visitors were allowed to approach to within a meter of the container, observing him as if he were an animal on display in a zoo.

Stewart envisioned the public experiment as a way to dramatize the extent to which people rely on the oxygen produced by plants. He explained to The Independent: "That box, this experiment, is the planet. People don't think of plants as our life support system without which we wouldn't be able to function and life wouldn't be able to function."

Stewart entered the container at 10pm on the night of Thursday, September 15. His colleagues then sealed him in. Besides the plants, Stewart also had a mobile phone, hammock, laptop, chemical toilet, and exercise bike with him.

The first few hours Stewart spent in darkness. As he did so, the oxygen levels in the container dropped from 21% down to 12.5%, the equivalent of the atmosphere at an altitude of 4500 metres. Then, early in the morning of September 16, his colleagues turned on a bank of lights, and the plants began to photosynthesize, supplying him with oxygen. The lights remained on for the rest of the experiment.

Researchers from the University College London's Centre for Altitude Space and Extreme Environment Medicine and the Royal Free Hospital constantly monitored Stewart and the atmosphere inside the container. When carbon dioxide levels fell too low for the plants, they had Stewart exercise on the bike, causing him to breath harder and produce more carbon dioxide. Stewart communicated with his colleagues via walkie talkie.

Stewart achieved his goal of remaining inside the tank for 48 hours, although he did suffer severe headaches and fatigue — effects of the oxygen deprivation. He also had trouble sleeping because of the constant lights, high humidity, and high temperature (25 degrees Celsius). He emerged from the container on the night of Saturday, September 17.